Voltage control system for electrostatic precipitators



July 28, 1959 H. A. WINTERMUTE 2,396,741

VOLTAGE CONTROL SYSTEM FOR ELECTROSTATIC PRECIPITATORS Filed Oct. 11. 1956 HIGH 6a VOLTAGE RECTIFIER v AOAMPS NW JVVV INVENTOR HARRY A WINTERMUTE ATTORNEY United States Patent VOLTAGE CONTROL SYSTEM FOR ELECTRO- STATIC PREClPIT-ATORS Harry A. Winter-mute, Plainfield, NJ., assignor to Research Corporation, New York, N.Y., a corporation 'of New York Application October 11, 1956, Serial No. 615,317

5 Claims. (Cl. 183-7) This invention relates to an improved system for antomatically controlling the operating voltage of electrical precipitators which must be used to treat gases under widely fluctuating conditions.

For the efiicient operation of a Cottrell type precipitator it is generally necessary to maintain a corona discharge between the discharge electrodes and the collecting electrodes of the precipitator. In general the higher the corona current flow, the greater will be the efficiency of gas cleaning and particle precipitation. However, corona discharges have a negative resistance characteristic, and this means that corona current flow increases at a very rapid rate with very slight voltage increase, which can very quickly lead to a dangerous degree of flashover or even complete breakdown between the electrodes. Furthermore, the voltage required to establish a given corona discharge is much less for certain gases than for others. I

In certain types of furnace operation, for example, blast furnace operation, normal furnace operation variations can at times produce a gas coming to the precipitator carrying a dust which is almost entirely finely divided red ore, while at other times the dust or fume is either dark or light gray in color. These dust conditions give widely different electrical operation, which is further complicated by the variation in dust concentration. This wide fluctuation renders it very difiicult to maintain at all times the correct electrical conditions in the precipitator for efficient operation and high recovery.

Operators are very much inclined to set the series primary transformer resistance so as to keep severe arcing within what they consider reasonable limits, which means that under most operating conditions the efficiency of the precipitator is very substantially reduced.

Due to the negative current characteristic of the required corona discharge, under the above conditions of widely different gas discharge, the required current in the primary supply circuit may vary widely, since the voltage required to establish a given corona discharge is much less for certain kinds of gases than for others. For example, conditions requiring a primary current variation from 25 amperes to 40 amperes at different times are encountered in typical blast furnace operation. Under these conditions, with known types of voltage control systems, it is very difficult to maintain the proper operating voltage at all times, since if the transformer primary voltage required for low voltage operation is main tained at the same level for high current operation, excessive arcing is produced. It is common to use a ballast resistor in series with the primary winding of the high voltage precipitator transformer, but this has been found inadequate to prevent improper operation under the severe operating conditions described above.

It is a primary object of the invention to provide a simple automatic voltage control system for precipitators which will obviate the above difiiculty by maintaining the precipitator always at the" correct operating voltage for maximum efficiency.

2,896,741 Patented July 28, 1959 "ice Another object is to provide a low-voltage precipitator control system entirely in the primary side of the transformer circuit, eliminating the problems of high voltage leads and circuits often found in precipitator control systems.

Still another object is to provide a precipitator control system which will operate correctly under conditions of heavy primary current fluctuation.

According to the invention, there is provided in series with the primary winding of the high voltage transformer a very low-ohmage impedance in the order of 1 ohm or less, the variation -in voltage drop across which corresponds to the variation in operating conditions produced by the different gas conditions described above, so that the corresponding variations in the residual voltage across the transformer primary winding now correspond to the requirements established by the different gas conditions. By maintaining the total voltage across the series combination, or primary winding and low-ohmage impedance, at a substantially constant value, the desired efiicient operating conditions can be maintained.

The invention may be described in general terms as including an electrical precipitator having a low-voltage input, a high-voltage step-up transformer, a high-voltage rectifier supplied by said transformer, and precipitator electrodes supplied by said rectifier; voltage control means for energizing the precipitator electrodes under a wide range of operating conditions requiring a large variation of input current to the primary of said transformer, comprising a voltage regulator connected between the lowvoltage input circuit and the transformer primary for adjusting the voltage supply to the primary, a low-ohmage impedance in series with said primary winding, and con trol means for adjusting said voltage control means to maintain the total voltage across the series combination of primary winding and said impedance substantially constant despite variations in primary current level, said impedance having a sufiiciently low value so that the voltage drop across it under the entire range of primary current values is less than 20 percent of the voltage across the primary winding.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings, in which:

Fig. 1 is a schematic circuit diagram of a typical precipitator system according to the invention;

Fig. 2 is a circuit diagram of the transformer primary circuit, showing the voltage distribution under high current conditions; and

Fig. 3 is a similar circuit diagram showing the voltage distribution under low current conditions.

Referring to Fig. 1, the operating line voltage, typically at 440 volts, is applied through terminals 2 through variaable induction regulator 3 which may typically provide a range of voltage variations from 300 volts to 600 volts; this voltage is applied through ballast resistor 4 to the primary winding 6b of high voltage transformer 6, in series with which is a low-ohmage impedance shown by way of example-as variable resistor 7, typically in the order of /3 ohm, and which may either be a fixed resistance or preferably an adjustable resistance as shown, in order to obtain a more precise control. The secondary winding 6a of transformer 6 is connected through a conventional high voltage rectifier to precipitator 9, in the usual fashion.

Connected across the series combination of transformer primary 6b and resistor 7 is the winding of a contact voltmeter 11 of any suitable type, adjusted to the required operating voltage, in this instance, 333 volts. If the voltage falls appreciably below this value, the circuit is closed from power supply leads 12 through winding 13a .of reversing motor 13, to adjust induction regulator 3 so as to raise the voltage. If the voltage rises appreciably above the preset yalue, the circuit is closed through winding 13b of reversing motor 13, to correspOndingly adjust the induction regulator 3 to lower the voltage. Thus thevoltage across primary 6b and resistor 7 is maintained very close to 333 volts. However, a constant voltage across the transformer primary would not produce the desired operating conditions, since under conditions of high current operation required for some types of gas treatment as explained above, the primary voltage should be lower than under conditions of low current operation, required for other operating conditions. This is provided by the above-described circuit, as will be clear by reference to Figs. 2 and 3.

, Fig. 2 shows the voltage distribution under conditions of high current operation, assumed to be 40 amperes. Since the voltage drop through the /3 ohm resistor 7 with 40 amperes of current flowing is 27 volts, the remaining voltage across the transformer primary 6b is 306 .volts. Similarly, as shown in Fig. 3, when the operating conditions of the precipitator require a primary currentof 25 ,arnperes, there will be only 17 volts drop through resistor 7, and the voltage drop across the transformer will now be 315 volts.

It will thus be apparent that the simple control circuit above described, produces the necessary voltage variationv across the transformer primary under conditions of both high and low primary current, required for efficient operation at all times.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims. For example, satisfactory results are obtained when the impedance in the primary winding 6b is from about 0.10 to about 2.5 ohms.

I claim:

1. In an electrical precipitator having a low-voltage input, a high-voltage step-up transformer, a high-volt age rectifier supplied by said transformer, and precipitator electrodes supplied by said rectifier; voltage control means for energizing the precipitator electrodes under a wide range of operating conditions requiring a large variation of input current to the primary of said transformer, comprising a voltage regulator connected between the low-voltage input circuit and the transformer primary for adjusting the voltage supply to the primary, a low-ohmage impedance in series with said primary winding, and means for adjusting said voltage regulator to maintain the total voltage across the series combination of primary winding and said impedance substantially constant despite variations in primary current level.

2. The invention according to claim 1, said impedance having a sufficiently low value so that the voltage drop across it under the entire range of primary current values is less than 20 percent of the voltage across the primary winding.

3. The invention according to claim 1 wherein said impedance comprises a resistor having a resistance value in the order of /3 ohm.

4. The invention according to claim 1, said adjusting means comprising voltage responsive means connected to respond to the voltage across said transformer primary and impedance, and means actuated by said voltage responsive means for adjusting said voltage regulator.

5. The invention according to claim 1, said adjusting means comprising a reversing motor having two windings, one for operation in each direction respectively, a driving connection between said motor and said voltage regulator to raise or lower the input voltage according to the direction of rotation of said motor, and voltage-responsive contactor means connected across said transformer primary and impedance in series to selectively actuate said windings in accordance with variations in voltage from a predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 2,392,434 Tnucksess Jan. 8, 1946 2,638,571 Schultz May 12, 1953 2,642,149 Backer et a1, June 16, 1953 

